Quadrature Surface Coils

Permittivity and performance of dielectric pads with sintered ceramic beads in MRI: early experiments and simulations at 3 T

“…The flip angle (α) at each voxel was obtained as where γ is the gyromagnetic ratio, the normalization factor Vτ (proportional to driving voltage times pulse duration) was determined by minimizing the difference (least mean square) between the experimental and simulated flip angle maps in the case with no dielectric material present (20). The intrinsic SNR of a short TR spoiled gradient echo sequence was calculated as (21, 22) where TR is 40 ms, T 1 is 291 ms, flip angle θ for this short TR spoiled gradient echo sequence is α/2 (equivalent to a nominal 30° pulse as used in experiment), and P diss is total power dissipated in the phantom, dielectric material, and receive coil with the single loop coil driven with unit current. Power dissipated in the phantom and dielectric material were determined with the numerical calculations, and power dissipated in the coil was determined using an analytical approximation.…”

Designing parallel transmit head coil arrays based on radiofrequency pulse performance

“…C, Proposed 4‐row‐by‐8‐loop‐per‐row 8‐channel dynamic multislice shimming array. D, The 2‐channel occipital lobe rFOV imaging array (similar to Figure 3.10 in Collins and Webb) with SPINS excitation trajectory. E, Proposed 3‐row‐by‐16‐loop‐per‐row 2‐channel occipital lobe rFOV imaging array with SPINS excitation trajectory.…”

“…The second application was rFOV occipital lobe excitation with SPINS excitation gradient trajectory . Two array models were simulated: a 2‐loop pTx array (similar to Figure 3.10 in Collins and Webb), shown in Figure D; and a pTx array with N c = 3 (rows) × 16 (coil per row) = 48 circular coil loop elements, shown in Figure E. In this scenario, the 48 candidate coil loops were pruned to coils and combined into an equivalent N cred = 2‐channel array using the proposed algorithm.…”

B1inhomogeneity correction of RARE MRI at low SNR: Quantitative in vivo19F MRI of mouse neuroinflammation with a cryogenically‐cooled transceive surface radiofrequency probe

“…[5][6][7][8][9][10] Further increases in SNR have been achieved with quadrature configurations, which provide a √ 2 SNR gain and better transversal B 1 homogeneity compared with linear polarized RF coils. [11][12][13] Quadrature CRPs are typically single-tuned for Xnuclei, 8 since dual-tunable capabilities would require electromagnetic decoupling between coil elements, [14][15][16] degrading signal sensitivity. This adds extra post-processing challenges when locating quantified 19 F signals in vivo.…”

“…Cryogenically cooled transceive surface RF probes (CRPs) have introduced a paradigm shift in preclinical imaging, providing substantial SNR gains compared with room‐temperature RF coils 5–10 . Further increases in SNR have been achieved with quadrature configurations, which provide a SNR gain and better transversal B 1 homogeneity compared with linear polarized RF coils 11–13 …”